Purex process of an aqueous process has been extensively used as a method for reprocessing spent nuclear fuel. According to the Purex process, the spent nuclear fuel is dissolved in nitric acid, and the nitric acid solution obtained is subjected to extraction with an organic solvent such as tributyl phosphate, thereby recovering uranium (U) and plutonium (Pu) (for example, refer to “Nuclear Chemical Engineering (separate volume IV) Chemical Engineering for Fuel Reprocessing and Radioactive Wastes Management”, edited by M. Benedict, et al., translated by Ryohei Kiyose, issued by the Nikkan Kogyo Shinbun-sha (daily industrial newspaper office), Dec. 29, 1983, pages 18 to 90).
As a dry process using no aqueous solution, two kinds of molten salt electrolysis processes have been developed. One of them is called Russian process and another is called ANL process. Both processes are named for a development country and a development organization, respectively. According to the Russian process, oxide fuel is melted in a molten salt of a chloride to deposit a U oxide on an electrode and precipitate a Pu oxide, thereby recovering both. According to the ANL process, metal fuel as it is or that obtained through prior reduction of oxide fuel into metal fuel is melted in a molten salt of a chloride, thereby recovering metal U and metal Pu on different electrodes, respectively.
As a dry reprocessing process other than the molten salt electrolysis processes, there is known a fluoride volatility process, in which reprocessing is effected making use of difference in volatility of fluorides. According to a known fluoride volatility process, U and Pu are recovered in a high purity making the most use of techniques such as distillation, partial condensation, adsorption and the like (for example, refer to “Nuclear power industry (Gensiryoku-Kogyo)”, issued by the Nikkan Kogyo Shinbun-sha (daily industrial newspaper office), Nov. 19, 2002, Vol. 17, No. 3, pages 53 to 58).
There is a process intended to improve said fluoride volatility process, wherein fluorination conditions are varied at the time of fluorination to carry out the fluorination one after another. According to the process, a uranium fluoride and a mixture of a uranium fluoride and a plutonium fluoride are recovered in a manner such that the former is in a high purity and the latter is in a low purity. Thereby, it is attempted to strength proliferation resistance and to increase an economical advantage due to omission of any purification step (for example, refer to JP-A-2000-284089).
Further, as a combination of the dry process and the aqueous process, there is a process, wherein the fluoride volatility process is combined with the Purex process. According to said combination process, it is attempted to recover U and a mixture of U and Pu to a high purity, and at the same time it is attempted to obtain an economical advantage due to miniaturization of devices (for example, refer to JP-A-2002-257980).